Communication system and method

ABSTRACT

A communication system including a first station having at least two first narrow beam antennas and a second station having at least two second narrow beam antennas. The first and second stations establish a first communication path for wireless communication via a pair of first and second narrow beam antennas. When communication via the first communication path is disturbed by obstacles, the first and second stations automatically establish at least one alternative communication path, which is spatially different from the first communication path, for wireless communication using the at least two first narrow beam antennas and the at least two second narrow beam antennas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 11/282,026,filed Nov. 17, 2005, now U.S. Pat. No. 7,680,517, the entire contents ofwhich are incorporated herein by reference and U.S. Ser. No. 11/282,026claims the benefit of priority under 35 U.S.C. §119 from European PatentApplication No. 05 001 674.0, filed Jan. 27, 2005 and European PatentApplication No. 04 027 554.7, filed Nov. 19, 2004.

BACKGROUND

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

The present invention relates to a communication system comprising thefeatures of the preamble of independent claim 1. Furthermore, thepresent invention relates to a corresponding communication method.

FIELD OF THE DISCLOSURE

Wireless communication is used in a large variety of technical fields.Typical examples are mobile phone, wireless LAN, walkie-talkies, radiosystems and point-to-point radio systems.

The communication radius covered by a respective communication systembasically depends on the technique used. Whereas GSM and UMTS areadapted for a communication radius up to about 10 km, wireless LANfrequently is restricted to about 100 m and the Bluetooth system usuallyis limited to about 20 m. The major influences on the communicationrange of a communication technique are the transmission frequency andoutput power used. Whereas only little absorption of electromagneticwaves in the atmosphere occurs at the transmission frequencies used forGSM/UMTS a significant absorption occurs in the 60 GHz range. Thus, the60 GHz range suits best for low and middle communication radiuses.

Furthermore, the kind of antenna used for a respective wirelesscommunication technique varies depend on a respective field ofapplication.

If large numbers of receivers have to be reached or the location of thereceiver is unknown or varies frequently, wide-beam antennas are used.

On the other hand, if only one or at least a very limited number ofreceivers have to be reached and the respective receiver(s) is/arestationary or at least quasi-stationary narrow-beam antennas can beused.

The utilisation of wide beam antennas in high data rate systems (e.g.over 1 Gbps) is problematic because of the multi-path fading effect.This multi-path fading effect is caused by differences of travellingtime between radio wave paths of the same transmission, as experiencedat the receiving station.

The multi-path fading effect is shown in FIG. 12.

As shown in FIG. 12, if wide beam antennas 121, 123, with e.g. a halfpower beam width (HPBW) of 100° are used for both a first station 120 ata sending side and a second station 122 at a receiving side and aline-of-sight 12 f (LOS) communication path is blocked by an obstacle124, there exist a lot of reflection paths 12 a, 12 b, 12 c, 12 d and 12e between the first station 120 and the second station 122 due to aplurality of reflecting surfaces 125, 126, 127, 128 and 129. The channeldelay spread might be over tens of symbol periods when the datatransmission rate is high (e.g. over 1 Gbps), which leads to severeinter-symbol interference (ISI) due to deep frequency selective fading.

As it is obvious from FIG. 12, the multi-path fading effect most likelyoccurs in city-centres or in indoor environments where a plurality ofreflecting surfaces 125, 126, 127, 128 and 129 (e.g. walls) are present.

Two conventional solutions exist for such kind of a no-line-of-sight(NLOS) user scenario:

One adopts channel equaliser including a linear, a decision feedback ora maximum likelihood sequence estimation (MLSE) equaliser. When thechannel delay spread is much longer than the symbol duration, theequaliser becomes complex and needs a lot of processing power.

Another solution is the orthogonal frequency division multiplexing(OFDM) technique, which is already adopted in wireless LAN systems.However, due to its inherent linear modulation and high peak to averageratio problems, the power consumption of a power amplifier (PA) usedwith the OFDM technique is very high.

Thus, both solutions need high-speed and complex signal processingcircuits.

In order to reduce the channel distortion, the adoption of a wide beamantenna 123 at one side and a sharp half power beam width (HPBW)steering antenna at another side for a no-line-of-sight (NLOS) userscenario is known as it is shown in FIG. 13.

The wide beam antenna 121 of the first station 120 of FIG. 12 isreplaced by a sharp beam antenna 131. Said sharp beam antenna 131 issteered to the optimum position (with feasible steering resolution),which could match to the strong reflection path 12 b and 12 c caused bythe reflecting surfaces 127 and 128. Due to the usage of said sharp beamantenna 131, the reflection signals 12 a, 12 d and 12 e shown in FIG. 13are not generated and thus can not reach the wide beam antenna 123 ofthe second station 122. Therefore, the channel delay spread isshortened.

Furthermore, another system concept is to use a pair of sharp beamsteering antennas 131 and 143 on both the transmitting first station 120and the receiving second station 122 side, which can be seen in FIG. 14.

Both sharp beam steering antennas 131 and 143 can be steered to anoptimum position, where strong reflection signals 12 c caused by areflecting surface 128 can be transmitted and received by both sharpbeam steering antennas 131 and 143 of the first and second station 120,122. As a result, the reflection signals 12 a, 12 b, 12 d and 12 e shownin FIG. 14 are not generated and thus cannot reach the second station122. Thus, the channel delay spread can be further shortened. Inaddition, considering the additional antenna gains obtained by bothsharp beam antennas 131 and 143, a strong received signal 12 c with arelatively small frequency selective fading channel can be obtained.

The usage of narrow beam antennas as it is described with respect toFIGS. 13 and 14 has the disadvantage that due to the limited beam widthemitted by a narrow beam antenna tracking of both antennas is verydifficult in no line of sight scenarios. Another problem is that a faststeering of the narrow beam antennas is necessary after a loss of thedirect or indirect communication path has occurred in order to keep thedata rate of the respective wireless communication system.

In summary the state of the art suffers from the followingdisadvantages:

Communication systems utilising wide beam antennas have to cope with themulti-path fading effect. This effect is even amplified when using highdata rates. To overcome the multi-path fading effect, complex equalisersor complex modulation scheme e.g., OFDM are required.

Communication systems using narrow beam antennas have fewer problemsconcerning the multi-path fading effect. With communication usingsystems narrow beam antennas it is very difficult to supportcommunication under non-line-of-sight conditions. Moreover, in acommunication system with narrow beam antennas on both sides, thereplacement of a broken link is very time consuming since a new suitablecommunication path has to be searched. This results in a significantdecrease of the data transmission rate.

SUMMARY

It is the object of the present invention to overcome the above-citeddisadvantages of the prior art and to provide a communication systemthat has a good availability even in indoor no-line-of-sight scenariosand guarantees a high data rate while having a simple and cheapstructure.

The above object is solved in a communication system comprising thefeatures of the preamble of independent claim 1 by the features of thecharacterising part of independent claim 1.

Furthermore, the above object is solved in a communication methodcomprising the features of the preamble of independent claim 16 by thefeatures of the characterising part of independent claim 16.

A communication system comprises a first station comprising a firstnarrow beam antenna and a second station comprising a second narrow beamantenna, wherein the first and second stations are adapted to establisha first communication path for wireless communication via said first andsecond narrow beam antennas. According to the present invention saidfirst and second stations are adapted to automatically establish atleast one alternative communication path for wireless communication viasaid first and second narrow beam antennas, said alternativecommunication path being spatially different from said firstcommunication path.

Thus, it is guaranteed that a new communication path automatically isgenerated in case an existing communication path is disturbed.

According to a preferred embodiment said first station comprises atleast two first narrow beam antennas and said second station comprisesat least two second narrow beam antennas, wherein the first and secondstations are adapted to establish at least one further communicationpath for wireless communication via said further first and second narrowbeam antennas while maintaining said first communication path, saidfurther communication path being spatially different from said firstcommunication path.

Thus, according to the present invention narrow beam antennas are usedon both sides of the communication path by the first and second station,respectively. Besides a possible line-of-sight communication path (link)at least one additional indirect communication path (link) is used toincrease the probability that at least one communication path isavailable all the times. Therefore, a high data rate can be guaranteedsince at least one communication path is indirect. Thus, the inventivecommunication system is capable to operate even under non line-of-sightconditions. Furthermore, the inventive communication system has a highsignal to noise ratio (SNR) due to a maximum ratio combining effectresulting from the plural communication paths. Although the inventivecommunication system is suitable for any environment where a sufficientnumber of reflecting surfaces are available, it is recommended that theinventive communication system works in indoor environments.

By the usage of narrow beam antennas, only, the inventive communicationsystem reduces the negative effects of multi-path selective fading.Moreover, the inventive communication system has a simple and cheapstructure since it does not require complex equalisers or modulationscheme, e.g., OFDM.

Preferably, said first station further comprises a first wide beamantenna and/or said second station further comprises a second wide beamantenna.

Thus, the first and/or second station is adapted to establish at least apreliminary communication path to the respective other station with alow data rate to agree on establishment of the at least two spatiallyseparated communication paths via said at least two first and secondnarrow beam antennas at a high data transmission rate.

It is beneficial if said first and second stations further comprisefirst and second sensors for determining a receive signal strengthindicator RSSI value of a signal received via a certain communicationpath by using a certain narrow beam antenna.

Thus, the first and second stations are adapted to detect the qualityand availability of a respective communication path. Moreover, by usingthe determined receive signal strength indicator RSSI value the firstand second stations are adapted to determine whether a respective firstand second narrow beam antenna is qualified for establishing acommunication path between said first and second station.

Favourably, said first and second stations further comprise first and/orsecond memories for storing said receive signal strength indicator RSSIvalue determined for a certain pair of narrow beam antennas for acertain communication path.

By storing said receive signal strength indicator RSSI values in firstand/or second memories all first and second narrow beam antennas of thefirst and second station are benchmarked with respect to theirqualification to establish a communication path in a respectiveenvironment. Thus, pre-recalled RSSI values stored in said first and/orsecond memories can be used to quickly establish a new communicationpath between said first and second station.

Moreover it is preferred that said receive signal strength indicatorRSSI value determined for a certain narrow beam antenna for a certaincommunication path is stored in first/second RSSI matrixes in said firstand/or second memories, respectively.

The usage of first/second RSSI matrixes to store said receive signalstrength indicator RSSI values allow an easy allocation of a respectiveRSSI value to a respective first or second narrow beam antenna.

Preferably said first station and/or said second station furthercomprise distinguishing means for distinguishing between a directcommunication path and an indirect communication path established by apair of first and second narrow beam antennas.

Furthermore, in the preferred embodiment it is beneficial if said firststation and/or said second station further comprise distinguishing meansfor distinguishing between a direct communication path established by apair of first and second narrow beam antennas and an indirectcommunication path established by another pair of first and secondnarrow beam antennas.

With the usage of distinguishing means the first and/or second stationsare further adapted to automatically differentiate line-of-sightscenarios from no-line-of-sight scenarios by the detection of thepresence or absence of a direct communication path between said firstand second station.

Preferably, said first and second stations further comprise determiningmeans for determining a relative distance between a respective narrowbeam antenna used for a direct communication path and a respectivenarrow beam antenna used for an indirect communication path.

With the usage of determining means said first and second stations areadapted to guarantee that said at least two communication paths betweensaid first and second stations are indeed spatially different. Inconsequence, the inventive communication system automatically ensuresthat the probability that all communication paths are blocked by asuddenly appearing obstacle is very low. Furthermore, said determinedrelative distance can be used when establishing new direct or indirectcommunication paths between said first and second station.

It is beneficial if said first and second stations further comprisefirst and second controllers for replacing a disturbed directcommunication path by using first and second narrow beam antennas havinga high RSSI and a low relative distance to the respective narrow beamantenna used for the disturbed direct communication path.

It is preferred that said first and second stations are stationary orquasi-stationary.

Thus, according to the present invention previously accomplished RSSImeasurements are used to quickly restore a disturbed communication path.Considering the fact that disruption of a communication path mostprobably is triggered by occasionally appearing obstacles and/orsometimes by station movements this guarantees a very good availabilityof at least one communication path in time.

Favourably, said first and second controllers further are adapted toreplace a disturbed indirect communication path by using first andsecond narrow beam antennas having a high RSSI and a middle or highrelative distance to the respective narrow beam antenna used for thedisturbed direct communication path.

In consequence, the inventive communication system automatically ensuresthat a disturbed indirect communication path is not erroneously replacedby a communication path parallel to the direct communication path.

If both the first and/or second stations are stationary orquasi-stationary reliable indirect communication path between said firstand second station can be established since a movement of reflectingsurfaces is rather unlikely.

Preferably, said first and second narrow beam antennas are switched beamantennas or adaptive antenna arrays or mechanical/manual steeringantennas.

According to a preferred embodiment said communication system is anindoor communication system.

The reason is that indoor environments usually comprise a plurality ofreflecting surfaces suitable for establishing indirect communicationpaths. A transmission frequency of about 60 GHz is usually reflected bywalls and other reflecting surfaces present in indoor environments.

It is beneficial if said first and second stations are adapted forbi-directional wireless communication using a transmission frequency ofabout 60 GHz via said communication paths.

According to the present invention a communication method for providingwireless communication between a first station and a second stationcomprises the following steps:

establishing a primary communication path via a first narrow beamantenna of said first station and a second narrow beam antenna of saidsecond station; and

establishing at least one alternative communication path via said firstnarrow beam antenna of said first station and said second narrow beamantenna of said second station, wherein said at least one secondarycommunication path is spatially different from said primarycommunication path.

Thus, it is guaranteed that a new communication path automatically isgenerated in case an existing communication path is disturbed.

According to a preferred embodiment said method further comprises thesteps of establishing at least one secondary communication path viaanother first narrow beam antenna of said first station and anothersecond narrow beam antenna of said second station, wherein said otherfirst and second narrow beam antennas are chosen in a way that said atleast one secondary communication path is spatially different from saidprimary communication path; and

performing wireless communication between said first and second stationvia said primary and/or said at least one secondary communication path.

Thus, according to the present invention at least two spatiallydifferent communication paths between said first and second stations aremaintained at the same time. Besides a possible line-of-sightcommunication path (link) at least one additional indirect communicationpath (link) is used to increase the probability that at least onecommunication path is available all the times. Due to the presence of atleast one communication path, a high data rate can be guaranteed.Moreover, the inventive communication method guarantees wirelesscommunication even under non line-of-sight conditions when noline-of-sight communication path is available. Furthermore, theinventive communication method results in a high signal to noise ratio(SNR) due to a maximum ratio combining effect resulting from the pluralcommunication paths. Although the inventive communication method issuitable for any environment where a sufficient number of reflectingsurfaces is available, the inventive communication method works best inindoor environments.

By the usage of narrow beam antennas for establishing communicationpaths, only, the inventive communication method reduces the negativeeffects of multi-path selective fading.

According to a preferred embodiment of the inventive communicationmethod the step of establishing a primary communication path comprisesthe steps of:

Sending test signals from said first station to said second station bysuccessively using all first narrow beam antennas of said first stationand by determining an individual receive signal strength indicator RSSIvalue of a test signal received by said second station for each firstnarrow beam antenna of said first station;

Selecting a respective first narrow beam antenna of said first stationhaving the best receive signal strength indicator RSSI value forestablishing the primary communication path;

Sending test signals from said first station to said second station byusing said selected first narrow beam antenna of said first station andreceiving said test signals by successively using all second narrow beamantennas of said second station, wherein an individual receive signalstrength indicator RSSI value of said test signal received by arespective second narrow beam antenna of said second station isdetermined for each second narrow beam antenna; and

Selecting a respective second narrow beam antenna of said second stationhaving the best receive signal strength indicator RSSI value forestablishing the primary communication path.

By using a received signal strength indicator RSSI value of a respectivefirst and second narrow beam antenna the inventive method establishesdirect and indirect communication paths between said first and secondstations in a quick and easy way.

In the preferred embodiment it is beneficial if the step of sending testsignals from said first station to said second station is performed by:

Sending a test signal from said first station to said second station byusing a first narrow beam antenna of said first station and a wide beamantenna of said second station;

Determining a receive signal strength indicator RSSI value of said testsignal received from said first narrow beam antenna; and

Sending a further test signal from said first station to said secondstation by using another first narrow beam antenna of said firststation, said test signal being received by said second wide beamantenna of said second station and determining another receive signalstrength indicator RSSI value of said further test signal received fromsaid other first narrow beam antenna until an individual receive signalstrength indicator RSSI value has been determined for every first narrowbeam antenna of said first station.

Furthermore, it is preferred that the step of establishing a primarycommunication path is initiated by the step of establishing apreliminary communication path between said first and second stationsvia a first wide beam antenna of said first station and a second widebeam antenna of said second station to detect the presence of arespective first and second station.

Usage of a wide beam antenna increases the velocity of establishment ofcommunication path between the first and second station via narrow beamantennas since it is not necessary to steer narrow beam antennas on bothsides of the communication path to establish a first communication pathbetween said first and second station.

Favourably, the sub-step of determining an individual receive signalstrength indicator RSSI value of a test signal received by a receivingstation for each narrow beam antenna of a sending station comprises thetransmission of the determined individual receive signal strengthindicator RSSI value from the receiving station to the sending station.

In consequence, the inventive communication method allows each first andsecond station to store the RSSI values for the first and second narrowbeam antennas belonging to a respective station.

It is beneficial if the individual receive signal strength indicatorRSSI values determined for the individual first and second narrow beamantennas are stored in first and second RSSI tables, respectively.

Preferably, the step of establishing at least one secondarycommunication path is performed by:

Determining a relative distance between a respective first/second narrowbeam antenna used for said primary communication path and unusedfirst/second narrow beam antennas;

Identifying unused first and second narrow beam antennas having asufficiently high receive signal strength indicator RSSI value and asufficient distance relative to the respective first/second narrow beamantenna used for said primary communication path; and

Establishing the at least one secondary communication path by using saididentified first and second narrow beam antennas.

In this respect it is preferred that the step of establishing the atleast one secondary communication path by using said identified firstand second narrow beam antennas is performed until no further unusedfirst and second narrow beam antennas having a sufficiently high receivesignal strength indicator RSSI value and a sufficient distance relativeto the respective first/second narrow beam antenna used for said primarycommunication path can be identified.

Favourably, the step of performing wireless communication between saidfirst and second station via said primary and/or at least one secondarycommunication path comprises the steps of:

Determining availability of the primary communication path and of the atleast one secondary communication path;

Using the primary communication path for wireless communication andreturning to the determining step if the primary communication path andthe at least one secondary communication path are available;

Using the primary communication path for wireless communication andestablishing at least one new secondary communication path if theprimary communication path is available and the at least one secondarycommunication path is unavailable;

Using the secondary communication path for wireless communication andestablishing a new primary communication path if the primarycommunication path is unavailable and the at least one secondarycommunication path is available; and

Returning to the step of establishing a primary communication path ifneither the primary communication path nor the at least one secondarycommunication path is available.

In this respect it is beneficial if the respective first and secondnarrow beam antennas having the highest available signal strengthindicator RSSI value are used in the step of establishing a new primarycommunication path.

Furthermore, in said step of performing wireless communication betweensaid first and second station via said primary and/or at least onesecondary communication path preferably a bi-directional wirelesstransmission using a transmission frequency of about 60 GHz isperformed.

The above object is further solved by a computer program productdirectly loadable into the internal memory of a microprocessor of anelectronic equipment, comprising software code portions for performingthe steps of one of the claims 26 to 27 when said product is run by saidmicroprocessor.

In this respect it is preferred if the computer program product isembodied on a computer readable medium.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the present invention arefurther explained by reference to the accompanying drawings, in whichlike reference numbers refer to like parts.

FIG. 1 schematically shows a preferred embodiment of the inventivecommunication system;

FIGS. 2A, 2B schematically show a side-view respectively front-view of across section along the axis S through four beams of communicationpaths;

FIG. 3 is a flowchart showing different states of the inventivecommunication system when initially establishing communication paths;

FIGS. 4A, 4B schematically show different states of the inventivecommunication system when establishing communication paths if steeringnarrow beam antennas are used;

FIG. 5 schematically shows a typical indoor environment for theinventive communication system according to the preferred embodiment;

FIGS. 6, 7 schematically explain typical disturbances of communicationpaths of the inventive communication system;

FIG. 8 shows a flow diagram of a first aspect of the inventivecommunication method;

FIG. 9 shows a flow diagram of a second aspect of the inventivecommunication method;

FIG. 10 shows a flow diagram of a third aspect of the inventivecommunication method;

FIG. 11 shows an example of RSSI tables used according to a preferredembodiment of the present invention;

FIG. 12 schematically shows a communication system using wide beamantennas according to the prior art;

FIG. 13 schematically shows a communication system using both wide andnarrow beam antennas according to the prior art; and

FIG. 14 schematically shows a communication system using narrow beamantennas according to the prior art.

DETAILED DESCRIPTION

In the following, a preferred embodiment of the inventive communicationsystem is explained by reference to FIG. 1.

The communication system 0 comprises a first station 1 comprising threefirst narrow beam antennas 31, 32, 33 and a second station 2 comprisingthree second narrow beam antennas 41, 42, 43.

In the present embodiment, both the first and second narrow beamantennas 31, 32, 33, 41, 42, 43 are smart antennas.

The first and second stations 1, 2 are adapted to establish at least onefirst communication path 7 a and one further communication path 7 b, 7 cfor wireless communication via said first and second narrow beamantennas 31, 32, 33, 41, 42, 43 at the same time.

Said further communication path 7 b, 7 c is spatially different fromsaid first communication path 7 a.

Thus, according to the present invention, usage of several pairs ofnarrow (sharp) beam antennas 31, 32, 33, 41, 42, 43 for both a sendingand receiving side of the station 1, 2 is proposed. Each first narrowbeam antenna 31, 32, 33 of the first station 1 is steered to meet acorresponding second narrow beam antenna 41, 42, 43 of the secondstation 2 along a corresponding communication path 7 a, 7 b, 7 c.Therefore, the usage of more than one pair of narrow beam antennas 31,32, 33, 41, 42, 43 realises path diversity for environments where nostatic communication path

In the present embodiment a communication path delay spread is shortenedand therefore the communication path becomes flat and relativelyfrequency non-selective.

As it is obvious from FIG. 1, a direct line of sight communication path7 d between said first and second station 1, 2 is blocked by an obstacle6.

Thus, said communication paths 7 a, 7 b, 7 c are indirect communicationpaths 7 a, 7 b, 7 c caused by reflecting surfaces 51, 52, 53, 54, 55.Each indirect communication path 7 a, 7 b, 7 c can be assumed as beingindependent. Thus, each indirect communication path 7 a, 7 b, 7 c can betreated as going through a frequency non-selective slow fading channel.The probability that all communication paths 7 a, 7 b, 7 c become weakor are interrupt completely at the same time is small. Thus, acommunication path diversity gain can be achieved.

If one strong line-of-sight (LOS) or no-line-of-sight (NLOS)communication path 7 a, 7 b, 7 c is intercepted, another communicationpath 7 a, 7 b, 7 c still can be used to guarantee the functionality ofthe communication system 0 as a whole.

When the attenuation of one or plural of the communication paths 7 a, 7b, 7 c is large, i.e., when one or plural of the communication paths 7a, 7 b, 7 c are in a deep fade, errors occur in reception and diversitytechniques can be used to improve the performance.

According to the above-described preferred embodiment of the inventivecommunication system several replicas of the same information signal aretransmitted to a receiving station 1, 2 over independently fadingcommunication paths 7 a, 7 b and 7 c. Thus, the probability that all thesignal components of the information signal will fade simultaneously isconsiderably reduced.

Those signals from independently fading communication paths 7 a, 7 b and7 c can be coherently combined to realize the spatial diversity

Each pair of narrow beam antennas 31, 32, 33, 41, 42, 43 can be treatedas one finger of the RAKE receiver in spread spectrum systems, which canbe adjusted based on the dynamic wireless environment. From atransmitting (Tx) side of the inventive communication system 0 (in thepresent embodiment the first station 1), only one transmitting chain isused and connected with several sending narrow beam antennas 31, 32 and33. From a receiving (Rx) side (in the present embodiment the secondstation 2), each receiving narrow beam antenna 41, 42, 43 is connectedto one receiving chain directly or preferably by a switch network. Byusing a switch network the number of required receiving chains can bereduced and can be adapted to the diversity order.

In comparison to smart antenna communication systems of the prior artthe present invention permits the usage of narrow beam steering antennas31, 32, 33, 41, 42, 43 on both sides of the communication path and thuson both the sending and the receiving side (stations 1 and 2). Thisreduces the multi-path fading effect and allows wireless communicationat a high data-rate. Furthermore, in common systems a communicationunder non-line-of-sight conditions is only achieved by utilising widebeam antennas. The inventive communication system 0 achievescommunication with high data rate under non-line-of-sight conditions byusing narrow beam antennas.

According to the preferred embodiment said first and second stations 1,2 further comprise first and second sensors 10, 11 for determining areceive signal strength indicator RSSI value of a signal received via acertain communication path 7 a, 7 b, 7 c by using a certain narrow beamantenna 31, 32, 33, 41, 42, 43.

The respective receive signal strength indicator RSSI values determinedby said sensors 10, 11 for a certain narrow beam antenna 31, 32, 33, 41,42, 43 for a certain communication path 7 a, 7 b, 7 c are stored infirst and second RSSI matrixes 14, 15 in first and second memories 12,13. Said first and second memories 12, 13 are connected to said sensors10, 11 of said first and second stations 1, 2, respectively.

According to an alternative embodiment (not shown in the figures), bothstations use only one common memory.

By using the RSSI values of the respective first and second RSSImatrixes 14, 15 stored in the respective first and second memories 12,13, the first and second station 1, 2 are adapted to distinguish betweena direct communication path 7 d established by a pair of first andsecond narrow beam antennas 31, 41 and an indirect communication path 7a, 7 b, 7 c established by another pair of first and second narrow beamantennas 32, 33, 42, 43.

Moreover, the first and second stations 1, 2 are adapted to determine arelative distance between a respective narrow beam antenna 31, 32, 33,41, 42, 43 used for a direct communication path 7 d and a respectivenarrow beam antenna 31, 32, 33, 41, 42, 43 used for an indirectcommunication path 7 a, 7 b, 7 c. This is performed by using therespective first and second RSSI matrix 14, 15 stored in the first andsecond memories 12, 13, too.

Furthermore, said first and second stations 1, 2 comprise first andsecond controllers 16, 17 for replacing a disturbed direct communicationpath 7 d by using first and second narrow beam antennas 31, 32, 33, 41,42, 43 having a high RSSI and a low relative distance to the respectivenarrow beam antenna 31, 32, 33, 41, 42, 43 used for the disturbed directcommunication path 7 d.

By using said first and second controllers 16, 17 the first and secondstation 1, 2 are further adapted to replace a disturbed indirectcommunication path 7 a, 7 b, 7 c by using first and second narrow beamantennas 31, 32, 33, 41, 42, 43 having a high RSSI and a middle or highrelative distance to the respective narrow beam antenna 31, 32, 33, 41,42, 43 used for the disturbed direct communication path 7 d. In thisrespect, a minimum reference distance can be defined to distinguishbetween a “low” and a “mid or high” distance. Replacement of disturbedor interrupted communication paths will be explained in detail byreference to the inventive communication method.

To distinguish between a direct communication path 7 d and an indirectcommunication path 7 a, 7 b, 7 c and to perform the replacement of adisturbed communication path, the first and second stations are providedwith suitable microcontrollers.

FIGS. 2A, 2B schematically show a side-view respectively front-view of across section along the axis S through four beams of four communicationpaths 7 a, 7 c, 7 d, 7 e.

As it is obvious from the FIGS. 2A and 2B the beams emitted by theplural first narrow band antennas 31, 32 of the first station 1 are notnecessarily separated completely, but might overlap. This is symbolisedby the reference number 7 ac of FIG. 2B.

FIG. 3 is a flowchart showing different states of the inventivecommunication system when initially establishing communication paths 7a, 7 b, 7 c and 7 d.

Further to the above described preferred embodiment, a first wide beamantenna 8 is connected to the first station 1 and a second wide beamantenna 9 is connected to said second station 2.

In the present embodiment, an adaptive antenna array is used as firstand second narrow beam antennas 31, 32, 33, 34, 41, 42, 43, 44.

According to an alternative embodiment shown in FIGS. 4A, 4B, steeringantennas are used as first and second narrow beam antennas 31, 32, 33,34, 41, 42, 43, 44. In order to find all sufficient direct and indirectcommunication paths, it is necessary to search all possible combinationsof positions of the first and second antennas 31, 32, 33, 34, 41, 42,43, 44. If the scanning range is 100°, for example and the half powerbeam width of the narrow beam steering antennas 31, 32, 33, 34, 41, 42,43, 44 is 20° the number of choices from each the first station 1 sideand the second station side is 5*5=25 and the total number ofcombinations for both of sides is 25*25=625.

For the initial establishment of a communication path the first andsecond wide beam antennas 8, 9 of the first and second station 1, 2 areused to find a respective opposite station 1, 2 and to agree onestablishment of a preliminary communication path LDR. This preliminarycommunication path LDR has a low data rate, only. Since the data rate islow, the channel distortion is negligible.

After the preliminary communication path LDR is established between thefirst and second wide beam antennas 8, 9 of the first and secondstations 1, 2, the first station successively transmits a test signalwith each of its first narrow beam antennas 31, 32, 33, 34. Only onefirst narrow beam antenna 31, 32, 33, 34 of the first station 1 is usedat the same time.

The opposite second station 2 determines a receive signal strengthindicator RSSI value for each test signal. This determined receivesignal strength indicator RSSI values are feedback by the second station2 to the first station 1 by utilising the second wide beam antenna 9 andthe respective first narrow beam antenna 31, 32, 33 and 34.

In case that steering narrow beam antennas are used as it is shown inFIGS. 4A, 4B, a beam direction of said antennas is steered until thesecond station 2 determines the highest receive signal strengthindicator RSSI value. If the scanning range is 100° and the half powerbeam width of the narrow beam antenna is 20°, the number of choices isonly 5*5=25.

Based on said receive signal strength indicator RSSI values the firststation 1 generates a first RSSI matrix 14, wherein each RSSI valuebelongs to a first narrow beam antenna 31, 32, 33, 34 of the firststation. Said first RSSI matrix 14 is stored in the first memory 12 ofthe first station 1.

Afterwards, the first station 1 selects the first narrow beam antenna 31that previously provided the strongest test signal to the second station2 by using said first RSSI matrix 14.

If the first station 1 uses a steering narrow beam antenna as it isshown in FIGS. 4A, 4B, the beam position of said steering narrow beamantenna is selected in correspondence with the position that previouslyprovided the strongest test signal to the second station 2.

By using said selected first narrow beam antenna 31 the first station 1is adapted to transmit and receive data to/from the second station 2.Thus, the first and second wide beam antennas 8, 9 are no longernecessary.

Afterwards the second station 2 starts to switch through its narrow beamantennas 41, 42, 43, 44 to receive test signals send by the firststation 1 via said selected first narrow beam antenna 31.

The second station 2 determines a receive signal strength indicator RSSIvalue for each test signal received from the first station 1. Based onthese RSSI values the second station 2 generates a second RSSI matrix 15and stores said second RSSI matrix 15 in the second memory 13. Thus, inaddition to the test signal no information exchange between the firststation 1 and the second station 2 is required at this stage of theprocedure.

If the second station 2 uses steering narrow beam antennas as it isshown in FIGS. 4A, 4B, a beam position of said steering narrow beamantennas is rotated until the second station 2 determines the highestreceive signal strength indicator RSSI value. If the scanning range is100° and the half power beam width of the narrow beam antenna is 20°,the number of choices at is also 5*5=25.

Alternatively, the second station 2 itself might send a test signal tothe first station 1 by switching through its second narrow beam antennas41, 42, 43, 44. The opposite first station 1 determines a receive signalstrength indicator RSSI value for each test signal and feedbacks saidRSSI values to the second station 2 by utilising the selected firstnarrow beam antenna 31. Based on the received RSSI values the secondstation 2 generates a second RSSI matrix 15 and stores said second RSSImatrix 15 in the second memory 13.

The second narrow beam antenna 41 with the best RSSI value according tothe second RSSI matrix 15 is selected by the second station 2 toestablishes a first high data rate (HDR) (preferably over 1 Gbps)communication path 7 a to the first station 1.

In addition to this first (primary) communication path 7 a, which mostprobably is the direct communication path in line-of-sight scenarios,the first and second stations 1, 2 automatically establish at least oneadditional further (secondary) communication path 7 b, 7 c by using theobtained first and second RSSI matrices 14, 15 and further first andsecond narrow beam antennas 32, 33, 42, 43, respectively. Said furthercommunication paths 7 b, 7 c are chosen in a way that they are spatiallydifferent from said first communication path 7 a and from one another.

As soon as a sufficient number of communication paths between the firstand second station 1, 2 has been established, the inventivecommunication system 0 switches into a tracking phase. Due to themovement of the first and/or second stations 1, 2 or of reflectingsurfaces 51, 52, 53, 54, 55, some strong communication paths 7 a, 7 b, 7c may be disturbed or blocked and thus fall below a predefined RSSIthreshold value.

It is preferred that at least one pair of narrow beam antennas from boththe first and second station 1, 2 continuously or regularly is used toupdate the first and second RSSI matrix to detect new strongcommunication paths. If a new strong communication path is detected, anexisting weaker communication path automatically is replaced by theinventive communication system 0.

FIGS. 4A, 4B basically correspond to FIG. 3.

FIGS. 4A, 4B schematically show different states of the inventivecommunication system 0 in case the first and second antennas 31, 41 ofthe first and second stations 1, 2 are manual or mechanical steeringnarrow beam antennas. It is noted that only one steering narrow beamantenna 31, 32 of each the first and second station 1, 2 is shown inFIGS. 4A, 4B. Nevertheless it is clear from the present invention thateach station 1, 2 is provided with at least two narrow beam antennas.

FIG. 5 schematically shows a typical indoor environment for theinventive communication system 0 according to the above preferredembodiment.

In FIG. 5, the first station 1 is a digital non-optical projector fortransmitting picture and sound data to the second station 2 being a LCDmonitor. Thus, the digital non-optical projector 1 is a wireless contentprovider for the LCD monitor 2.

Both the digital non-optical projector 1 and the LCD monitor 2 arequasi-stationary. Only the non-optical projector 1 might be movedoccasionally. The LCD monitor 2 is fixed to the wall.

In this scenario, a loss of a communication path 7 a, 7 c, 7 d is mostprobably initiated by an appearing obstacle 6, e.g. a moving person, asit is shown in FIGS. 6 and 7.

One direct communication path 7 d and two indirect communication paths 7a, 7 c are provided to guarantee wireless communication between thefirst station 1 and the second station 2. In consequence it is unlikelythat all communication paths 7 a, 7 c, 7 d are interrupted due to anappearing obstacle 6 at the same time.

In FIG. 5 bi-directional wireless communication using a transmissionfrequency of about 60 GHz is performed by the first and second station1, 2, respectively.

It is obvious from FIG. 5 that the inventive communication system 0works especially well with indoor environments due to the high number ofreflecting surfaces and the resulting high number of possible spatiallyseparated communication paths.

FIGS. 6, 7 schematically explain typical disturbances of communicationpaths of the inventive communication system in the typical indoorenvironment shown in FIG. 5.

In FIG. 6 a person 6 enters the indoor environment and causes a loss ofthe indirect communication path 7 a. This disturbed indirectcommunication path 7 a instantly is replaced by the inventivecommunication system 0 by a new indirect communication path 7 b. If thedisturbed indirect communication path 7 a cannot be replaced, still twoworking communication paths 7 d, 7 c are available. Thus, aninterruption of the communication and a decrease of the datatransmission rate is avoided.

FIG. 7 shows a non-line-of-sight situation that occurs when the person 6moves in-between the first and second stations 1, 2. In consequence,only indirect communication paths 7 a, 7 b, 7 c are provided. Althoughthe direct communication path 7 d is lost, the data transmission rate ismaintained due to the presence of indirect communication paths 7 a, 7 band 7 c.

Although the communication system 0 according to the above describedpreferred embodiment comprises a first station 1 comprising three firstnarrow beam antennas 31, 32, 33 and a second station 2 comprising threesecond narrow beam antennas 41, 42, 43, each it is within the scope ofthe present invention that both the first station 1 and the secondstation 2 comprise one single first and second narrow beam antenna 41,31, each.

In this case, said first and second stations 1, 2 are adapted toautomatically establish at least one alternative communication path 7 b,7 c for wireless communication via said first and second narrow beamantennas 31, 41, wherein said alternative communication path 7 b, 7 c isspatially different from said first communication path 7 a.

Establishment of said alternative communication path is performed bychanging the respective steering direction (orientation) of said firstand second narrow beam antennas 31, 41. Thus, said first and secondnarrow beam antennas 31, 41 have to be steerable antennas (e.g. antennaarrays, smart antennas, or antennas having a motor), respectively.

Thus, it is guaranteed that a new communication path 7 b or 7 c isautomatically generated in case the first communication path 7 a isdisturbed.

FIGS. 8, 9 and 10 show different aspects of a preferred embodiment ofthe inventive communication method.

In general, the inventive communication method for providing wirelesscommunication between a first station 1 and a second station 2 comprisesthe steps of:

Establishing a primary communication path 7 a, 7 d via a first narrowbeam antenna 31 of said first station 1 and a second narrow beam antenna41 of said second station 2, establishing at least one secondarycommunication path 7 b, 7 c via another first narrow beam antenna 32,33; 32, 33, 34, 3 n of said first station 1 and another second narrowbeam antenna 42, 43; 42, 43, 44, 4 n of said second station 2, whereinsaid other first and second narrow beam antennas 32, 33, 42, 43; 32, 33,34, 3 n, 42, 43, 44, 4 n are chosen in a way that said at least onesecondary communication path 7 b, 7 c is spatially different from saidprimary communication path 7 a, 7 d and performing wirelesscommunication between said first and second station 1, 2 via saidprimary communication path 7 a, 7 d and/or said at least one secondarycommunication path 7 b, 7 c.

The step of establishing a primary communication path 7 a, 7 d and thestep of establishing at least one secondary communication path 7 b, 7 chas already been explained in detail with respect to FIG. 3.

FIG. 8 displays a substitution algorithm that takes place when acommunication path 7 a, 7 b, 7 c, 7 d goes down.

According to the substitution algorithm in a first step 81 it is checkedwhether all communication paths (links) are down.

If all communication paths are down an initial communication pathestablishment procedure is started in step 82 and the substitutionalgorithm is terminated. This initial communication path establishmentprocedure has already been explained in detail with respect to FIGS. 3,4A and 4B.

If at least one communication path is maintained it is checked in thefollowing step 83 whether an indirect communication path is down.

If so, an indirect communication path substitution algorithm is statedin the following step 85 and the substitution algorithm is terminated.

If no indirect communication path is down, a direct communication pathsubstitution algorithm is stated in step 84 and the substitutionalgorithm is terminated.

Thus, in case a communication path goes down at a point in time, (e.g.due to an appearing obstacle 6) the substitution algorithm checks if thebroken communication path is an indirect or and direct communicationpath to perform the appropriate sub-algorithm.

Therefore, the two main components of this substitution algorithm arethe indirect communication path substitution sub-algorithm 85 and thedirect communication path substitution sub-algorithm 84. Thesesubstitution sub-algorithms are shown in detail in FIGS. 9 and 10,respectively.

In the present embodiment the above substitution algorithm is startedautomatically as soon as a link loss is detected during the regular RSSImeasurements.

The indirect communication path substitution sub-algorithm 85 is shownin more detail in FIG. 9.

In a first step 851 of the indirect communication path substitutionsub-algorithm 85 a weighting function is applied on the RSSI valuesstored in the first and second RSSI matrix 14, 15 to create asubstitution matrix. The purpose of the weighting function is to avoidneighbouring beams to the direct communication path, i.e. additionalline-of-sight communication paths.

For example, in FIGS. 2A, 2B four neighbouring beams emitted by narrowbeam antennas 31, 32, 34, 35 are displayed. In order to cover the wholearea there frequently are some overlaps of the communication paths 7 a,7 c, 7 d and 7 e of the respective narrow beam antennas 31, 32, 34, 35.Such an overlap is for example area 7 ac. The cross-section of the fourcommunication paths 7 a, 7 c, 7 d and 7 e shows that there are severalof these overlaps. If the second station 2 is located within one ofthese overlaps, the measured RSSI values of the adjacent beams ofadjacent communication paths 7 a, 7 c, 7 d, 7 e will have almost thesame high RSSI value. In consequence it is possible that all narrow beamantennas with the highest RSSI values belong to basically oneline-of-sight communication path. In case an obstacle 6 moves in-betweenthe first and second station 1, 2 there is a high risk said allline-of-sight communication paths are disturbed at the same time.

Thus, in order to find a narrow beam antenna for establishing anindirect communication path, i.e. non-line-of-sight communication path,it is not sufficient to consider the RSSI values, only.

To overcome this problem, a weighting function is used. The weightingfunction adds some additional value to the measured RSSI values,depending on a relative distance of a respect narrow beam antenna to anarrow beam antenna currently used for a direct communication path.Those narrow beam antennas are favoured for establishing a new indirectcommunication path, which have both a high RSSI value in the respectivefirst and second RSSI matrix and also some distance to said narrow beamantenna currently used for said direct communication path. Inconsequence, the weighting function bases on a determination of arelative distance between a respective first/second narrow beam antennaused for a direct (primary) communication path and unused first/secondnarrow beam antennas intended for the establishment of new indirectcommunication paths.

It is obvious that the creation of the substitution matrix by applyingthe weighting function on the first and second RSSI matrix 14, 15alternatively can be performed before an indirect communication pathgoes down. Since it is preferred that the first and second stations 1, 2gradually update their corresponding first and second RSSI matrix 14, 15by measurements of RSSI values, it is also preferred to update thesubstitution matrix at the same time. This parallel update of both theRSSI matrix and the substitution matrix speeds up a subsequent searchfor new indirect and direct communication paths significantly.

In the following step 852 a pair of first and second narrow beamantennas with the highest values in the substitution matrix is chosen.

Afterwards, in step 853 it is tried to establish a communication pathvia said chosen pair of narrow beam antennas. This is performed byupdating the corresponding RSSI value of said chosen narrow beamantennas in the respective first/second RSSI matrix 14, 15 in step 854.

In step 855 it is decided whether the measured RSSI values reach apredefined threshold value and thus are sufficiently high to justify useof the chosen pair of narrow beam antennas for establishment of a newindirect communication path.

If the measured RSSI values reach said predefined threshold value thenew indirect communication path is established by using said chosen pairof narrow beam antennas and the method is terminated.

If one or both of the measured RSSI values are below said predefinedthreshold value the corresponding values in the respective substitutionmatrix are set to ‘0’ to mark this previously chosen pair of narrow beamantennas as ineligible in step 856.

In the following step 857 it is decided if there still exist narrow beamantennas (elements) with a value >0 in the substitution matrix.

If so, the method loops to step 852 and selects the pair of narrow beamantenna with the highest value in the substitution matrix. Thus, thealgorithm tests the remaining narrow beam antennas, in sequence of theirvalues in the substitution matrix until an appropriate pair of narrowbeam antennas is found or not further suitable narrow beam antennasexist.

If it is decided in step 857 that no narrow beam antennas with avalue >0 exists in the substitution matrix, it is currently not possibleto replace the broken indirect communication path and the substitutionis postponed in step 858.

If during the regular gradual update of the RSSI matrix a possiblenarrow beam antenna or pair of narrow beam antennas for a replacementemerges, i.e. has an RSSI value above a certain threshold, thecommunication path is established instantly by the above describedindirect communication path substitution sub-algorithm 85.

The direct communication path substitution sub-algorithm 84 is shown inmore detail in FIG. 10.

This direct communication path substitution sub-algorithm 84 worksslightly different from the indirect communication path substitutionsub-algorithm 85. Instead of a substitution matrix, the RSSI matrix 14,15 is used directly.

In a first step 841, it is checked if one of the narrow beam antennasnext to a respective narrow beam antenna formally used for the brokendirect communication path can be used as a replacement. Thus, the pairof neighbouring first and second narrow beam antenna with the highestRSSI value is selected (provided that the RSSI value is above thepredefined minimum threshold).

Afterwards, in step 842 it is tried to establish a new directcommunication path.

During this procedure the RSSI values of the chosen pair of narrow beamantennas is measured and the respective first/second RSSI matrix 14, 15is updated in step 843.

In step 844 it is decided whether the measured RSSI values reach thepredefined minimum threshold.

If the measured RSSI values reach the predefined minimum threshold thechosen pair of narrow beam antennas is used for the established newdirect communication path and the sub-algorithm is terminated.

If the measured RSSI values are below the predefined minimum thresholdit is tested in step 845 whether other eligible narrow beam antennasneighbouring the narrow beam antenna formally used for the disturbeddirect communication path exist.

If other eligible narrow beam antennas neighbouring the narrow beamantenna previously used for the disturbed direct communication pathexist the method loops to step 841 and selects the pair of neighbouringfirst and second narrow beam antennas with the highest RSSI value in thecorresponding RSSI table 14, 15.

If no other eligible narrow beam antennas neighbouring the narrow beamantenna previously used for the disturbed direct communication pathexist it is currently not possible to replace the broken directcommunication path with a new direct communication path adjacent to theold direct communication path.

In consequence, the indirect communication path substitutionsub-algorithm 85 is entered in step 846 and the direct communicationpath substitution sub-algorithm 84 is terminated.

According to another preferred embodiment a pair of narrow beam antennaspreviously used for the disturbed direct communication is tested morefrequently for establishing a new direct communication path than otherfirst and second narrow beam antennas of the first and second stations.

If during the regular updates of the RSSI matrixes 14, 15 a possible newdirect communication path emerges, i.e. measured RSSI value or narrowbeam antennas are considerably higher than the RSSI values of othernarrow beam antennas in the RSSI matrix an indirect communication pathautomatically is replaced by a new direct communication path.

The communication path substitution algorithm of FIGS. 9, 10 bases onthe fact that in a quasi-static indoor environment the indirectcommunication paths will work almost all the time, since the reflectingsurfaces 51, 52, 53, 54, 55 as well as the first and second stations 1,2 will not move very often.

Furthermore, a lost communication path 7 a, 7 b, 7 c, 7 d usually can besubstituted by using the RSSI values previously stored in the first andsecond RSSI matrix 14, 15 in a short time.

As said before, in the first and second RSSI matrix 14, 15 each elementbelongs to a first and second narrow beam antenna 31, 32, 33, 34, 3 n,41, 42, 43, 44, 4 n of the first and second stations 1, 2, respectively.

As it has been explained in detail by reference to FIG. 3 the RSSImatrix 14, 15 is created during the initial link establishment procedure82 and is updated gradually during the communication. When a loss of acommunication path 7 a, 7 b, 7 c, 7 d is detected, the inventivecommunication method automatically checks the eligible (unused) narrowbeam antennas 31, 32, 33, 34, 3 n, 41, 42, 43, 44, 4 n with respect totheir corresponding RSSI values stored in the respective RSSI matrix 14,15 to replace the disturbed communication path.

Due to said RSSI values stored in said first and second RSSI matrix thesearch for a suitable new communication path is acceleratedsignificantly.

In this respect it is assumed that the measured RSSI values of narrowbeam antennas used for a direct communication path are considerablyhigher than the measured RSSI value of narrow beam antennas used for anindirect communication path. According to the present invention thisfact is used to distinguish direct communication paths form indirectcommunication paths.

In summary, both an acquisition and tracking algorithm are proposed tofacilitate the steering of narrow beam antennas during the acquisitionof communication paths. By using these algorithm the calculationcomplexity is significantly reduced.

FIG. 11 shows examples of RSSI tables 14, 15, 14′, 15′ used to replacebroken communication paths 7 a, 7 b, 7 c, 7 d (links) according to theembodiment of FIGS. 4A, 4B.

Each RSSI table 14, 15, 14′, 15′ comprises a receive signal strengthindicator value for each narrow beam antenna 31, 32, 33, 34, 3 n, 41,42, 43, 44, 4 n of a respective station 1, 2.

Thus, according to the RSSI tables 14, 15, 14′, 15′ shown in FIG. 11,both the first and second station 1, 2 comprise 16 distinguishablenarrow beam antennas.

According to an alternative embodiment not shown in the figures thefirst and second station comprise different numbers of narrow beamantennas. In consequence the respective first and second RSSI tableshave different sizes.

In the present embodiment, some of the values of the RSSI tables 14, 15,14′, 15′ relate to “virtual” narrow beam antennas and thus to differentsteering positions of one single narrow beam antenna as it is shown inFIGS. 4A, 4B.

Alternatively, all values of the RSSI tables may relate to “real” narrowbeam antennas as it is shown in FIG. 3.

In the present embodiment, the first station 1 comprises four firststeering narrow beam antennas 31, 32, 33, 34. Said first narrow beamantennas 31, 32, 33, 34 are arranged in a square and can be steeredmanually to four adjacent positions, each. Thus, four RSSI values ofeach subsection 14 a, 14 b, 14 c and 14 d relate to one narrow beamantenna 31, 32, 33, 34 of the first station 1, respectively.

Furthermore, in the present embodiment, the second station 2 comprisesfour steering narrow beam antennas 41, 42, 43, 44. Said narrow beamantennas 41, 42, 43, 44 are arranged in a horizontal line and can besteered mechanically to four vertical positions, respectively. Thus,four RSSI values of each column 15 a, 15 b, 15 c and 15 d relate to onenarrow beam antenna 41, 42, 43, 44 of the second station 2,respectively.

Alternatively to steering antennas switched beam antennas or adaptiveantenna arrays might be used. With respect to the embodiment shown inFIG. 11, the adaptive antenna array of both the first and second stationwould consist of 4.times.4 narrow beam antennas.

These RSSI tables 14, 15, 14′, 15′ are stored in the memories 12 and 13of the respective first and second stations 1, 2 and thus on both sidesof the communication paths.

As it is obvious from FIG. 11, the sections 14 b and 15 b of the RSSItables 14 and 15 show the highest RSSI values “39” and “40”,respectively. These RSSI values are significantly higher than thefurther RSSI values of the RSSI tables 14 and 15. In consequence it isassumed that these values belong to a direct communication path. Thus,the direct communication path is established via the first narrow beamantenna 32 relating to section 14 b and the second narrow beam antenna42 relating to section 15 b.

Two further pairs of high RSSI values can be identified in the RSSItables 14 and 15: A first pair of RSSI values “15” and “15” is found insections 14 c and 15 d of the RSSI tables 14 and 15. These RSSI valuesare significantly lower than the highest RSSI value of the RSSI tables14 and 15. Furthermore, a relative distance of the steering direction ofthe corresponding first and second narrow beam antennas 33 and 44 to thesteering direction of the first and second narrow beam antennas 32 and42 used for the direct communication path is above a predefinedreference value and thus high. In consequence it is assumed that thesevalues belong to an indirect communication path. Thus, a first indirectcommunication path is established via the first narrow beam antenna 33relating to section 14 c and the second narrow beam antenna 44 relatingto section 15 d.

A second pair of high RSSI values “13” and “12” is found in sections 14d and 15 a of the RSSI tables 14 and 15. Based on the above-describedcriteria it is assumed that these values belong to a further indirectcommunication path. Thus, a second indirect communication path isestablished via the first narrow beam antenna 34 relating to section 14d and the second narrow beam antenna 41 relating to section 15 a.

Summarising, RSSI tables 14 and 15 show a state of the inventivecommunication system 0 in which one direct communication path and twoindirect communication paths have been established to connect the firstand second station 1, 2.

If, for example, the direct communication path goes down (e.g. due to anappearing obstacle 6), the corresponding RSSI values become “0” as it isshown in the RSSI tables 14′ and 15′. Since the indirect communicationpaths are maintained, the information transmission rate is not reduceddue to the missing direct communication path.

To replace the disturbed direct communication path by a newcommunication path the RSSI tables 14 and 15 of the first and secondstation 1, 2 are compared to identify high pairs of RSSI values.

Firstly, a pair of RSSI values of “9” and “10” of sections 14′d and 15′dof the RSSI tables 14′ and 15′ is identified (see “Test 1”). Since thecorresponding narrow beam antennas 34 and 44 of the first and secondstations 1, 2 are currently used to establish a strong indirectcommunication path, this test is skipped.

Secondly, a pair of RSSI values of “5” and “5” of sections 14′a and 15′bof the RSSI tables 14′ and 15′ is identified (see “Test 2”). Thecorresponding narrow beam antennas 31 and 42 of the first and secondstations 1, 2 are not used. The respective steering directions of thecorresponding first and second narrow beam antennas 31 and 42 areadjacent to the respective steering directions of the first and secondnarrow beam antennas 32 and 42 that have been used for the interrupteddirect communication path. In consequence, the relative distance to therespective narrow beam antennas 32 and 42 previously used for the directcommunication path is very low. Thus, it is assumed that these RSSIvalues belong to a disturbed direct communication path. Nevertheless thecommunication path is tested. If the test results in RSSI values below apredefined threshold, no communication path is established. If thepredefined threshold value is reached, a new direct communication pathis established.

Thirdly, a pair of RSSI values of “4” and “3” of sections 14′a and 15 dof the RSSI tables 14′ and 15′ is identified (see “Test 3”). Since thecorresponding narrow beam antennas 31 and 44 of the first and secondstations 1, 2 are currently used to establish other indirectcommunication paths, this test is skipped.

Thus, the possible substitution communication paths are tested accordingto the decreasing RSSI values of the first and second narrow beamantennas in the first and second RSSI matrix, respectively.

If all tests are negative it is assumed that the position of the firstor second station 1, 2 has changed significantly. In case allcommunication path go down a restart of the initial communication pathestablishment procedure is necessary.

Since it is not necessary to test all possible antenna configurationsdue to the usage of the RSSI tables 14, 15, there is a high probabilityto find a new communication path in a very fast and easy way.

In the above described preferred embodiment of the inventive method asecond pair of first and second narrow beam antennas 32, 33, 34, 3 n,42, 43, 44, 4 n is provided to establish said at least one secondarycommunication path 7 b, 7 c in addition to said primary communicationpath 7 a, 7 d. Wireless communication between said first and secondstation 1, 2 is performed via said primary communication path 7 a and/orsaid at least one secondary communication path 7 b, 7 c.

Notwithstanding it is within the scope of the present invention toestablish said secondary communication path 7 b, 7 c by using said firstpair of first and second narrow beam antennas 31, 41, only. Thus, nofurther narrow beam antennas are required.

In this case said at least one alternative communication path 7 b, 7 cis established via said first narrow beam antenna 31 of said firststation 1 and said second narrow beam antenna 41 of said second station2. Similar to the above embodiment said at least one secondarycommunication path 7 b, 7 c has to be spatially different from saidprimary communication path 7 a; 7 d. Thus, said first and secondantennas 31, 41 have to be steerable antennas.

In this respect it is obvious that interruption of the primarycommunication path 7 a; 7 d preferably is detected before said at leastone alternative communication path 7 b, 7 c is established. The reasonsis that establishment of the alternative communication path 7 b, 7 cautomatically interrupts the primary communication path 7 a; 7 d. Thus,the alternative communication path 7 b, 7 c preferably is establishedonly if said primary communication path 7 a; 7 d is not longeravailable. It is preferred that said alternative communication path 7 b,7 c is established automatically if interruption of the primarycommunication path 7 a; 7 d is detected.

It is preferred that the above described method is implemented into acomputer program product directly loadable into the internal memory of amicroprocessor of an electronic equipment. Said computer program productpreferably comprises software code portions for performing the steps ofthe above described method when said product is run by saidmicroprocessor.

In this respect it is preferred if the computer program product isembodied on a computer readable medium.

In summary, the present invention discloses a wireless communicationsystem and method especially suitable for indoor short-rangeapplications. The inventive communication system and method guarantees ahigh data rate even for no line of sight (NLOS) user scenarios.

The main advantages in comparison to the prior art are that theinventive communication system and method reduces the negative effectsof multi-path propagation like fading by using narrow beams and allowswireless communication at a high data rate without frequentinterceptions even under non-line-of-sight conditions. Due to the usageof narrow beam antennas on both sides of the communication path it isnot necessary to use complex and expensive equalisers. Furthermore, themaximum ratio combining effect results in a higher signal to noise ratio(SNR) compared to the prior art. Moreover, the inventive trackingalgorithm of the inventive communication method provides a quick andefficient substitution of broken links.

1. A communication system comprising: a first station comprising aplurality of first antennas providing a plurality of first antenna beamdirections; and a second station comprising a plurality of secondantennas providing a plurality of second antenna beam directions;wherein said first and second stations are configured to establish afirst communication path for wireless communication via a first one ofsaid plurality of said first antennas and a first one of said pluralityof said second antennas, and said first and second stations areconfigured to find at least one alternative communication path forwireless communication via said first one of said plurality of firstantennas and said first one of said plurality of said second antennaswhen the first communication path is blocked, said alternativecommunication path being different from said first communication path.2. A communication system according to claim 1, wherein the first andsecond stations are configured to establish at least one furthercommunication path for wireless communication via a second one of saidplurality of first antennas and a second one of said plurality of saidsecond antennas while maintaining said first communication path, said atleast one further communication path being different from said firstcommunication path.
 3. A communication system according to claim 1,wherein said first station further comprises a first wide beam antennaand/or said second station further comprises a second wide beam antenna.4. A communication system according to claim 1, wherein said first andsecond stations further comprise first and second sensors fordetermining a receive signal strength indicator RSSI value of a signalreceived via a certain communication path by using a certain antennadirection.
 5. A communication system according to claim 4, wherein saidfirst and second stations further comprise first and/or second memoriesfor storing said receive signal strength indicator RSSI value determinedfor a certain pair of antenna beam directions for a certaincommunication path.
 6. A communication system according to claim 5,wherein said receive signal strength indicator RSSI value determined fora certain antenna beam direction for a certain communication path isstored in first/second RSSI matrixes in said first and/or secondmemories, respectively.
 7. A communication system according to claim 1,wherein said first station and/or said second station further comprisedistinguishing means for distinguishing between a direct communicationpath and an indirect communication path established by a pair of firstand second antenna beam directions.
 8. A communication system accordingto claim 1, wherein said first station and/or said second stationfurther comprise distinguishing means for distinguishing between adirect communication path established by a pair of first and secondantenna beam directions and an indirect communication path establishedby another pair of first and second antenna beam directions.
 9. Acommunication system according to claim 1, wherein said first and secondstations further comprise determining means for determining a relativedistance between a respective antenna beam direction used for a directcommunication path and a respective antenna beam direction used for anindirect communication path.
 10. A communication system according toclaim 9, wherein said first and second stations further comprise firstand second controllers for replacing a blocked direct communication pathby using first and second antenna beam directions having a high RSSI anda low relative distance to the respective antenna beam direction usedfor the blocked direct communication path.
 11. A communication systemaccording to claim 10, wherein said first and second controllers furtherare configured to replace a blocked indirect communication path by usingfirst and second antenna beam directions having a high RSSI and a middleor high relative distance to the respective antenna beam directions usedfor the blocked direct communication path.
 12. A communication systemaccording to claim 1, wherein said first and second stations arestationary or quasi-stationary.
 13. A communication system according toclaim 1, wherein said plurality of first and second antennas areswitched beam antennas or adaptive antenna arrays or mechanical/manualsteering antennas.
 14. A communication n system according to claim 1,wherein said communication system is an indoor communication system. 15.A communication system according to claim 1, wherein said first andsecond stations are adapted for bi-directional wireless communicationusing a transmission frequency of about 60 GHz via said communicationpaths.
 16. A communication system according to claim 1, wherein thesecond station is configured to coherently combine information signalstransmitted on the first communication path and on each of the at leastone alternative communication path.
 17. A communication system accordingto claim 16, wherein the information signals transmitted on the firstcommunication path and on each one of the at least one alternativecommunication path are the same.
 18. A communication system according toclaim 1, wherein the second station is operable as a RAKE receiver,whereby each second antenna used for establishing said firstcommunication path or said at least one alternative communication pathcorresponds to a finger of the RAKE receiver.
 19. A communication systemaccording to claim 1, wherein the second station comprises a RAKEreceiver including a plurality of receiver chains and each secondantenna is directly connected to one receiver chain.
 20. A communicationsystem according to claim 1, wherein the second station comprises switchnetwork and a RAKE receiver comprising a plurality of receiver chains,wherein the number of receiver chains is smaller than the number ofsecond antennas and each second antenna is connectable to a receiverchain via the switch network.
 21. A communication method for providingwireless communication between a first station comprising a plurality offirst antennas providing a plurality of first antenna beam directionsand a second station comprising a plurality of second antennas providinga plurality of second antenna beam directions, the method comprising:establishing a primary communication path via a first one of saidplurality of first antennas and a first one of said plurality of saidsecond antennas; and establishing at least one alternative communicationpath via said first one of said plurality of first antennas and saidfirst one of said plurality of second antennas when the primarycommunication path is blocked, said at least one alternativecommunication path being different from said primary communication path.22. A communication method according to claim 21, further comprising:establishing at least one secondary communication path via a second oneof said plurality of first antennas and a second one of said pluralityof said second antennas, wherein said at least one secondarycommunication path is different from said primary communication path.23. A communication method according to claim 21, wherein establishing aprimary communication path comprises: sending test signals from saidfirst station to said second station by successively using all firstantenna beam directions of said first station and by determining anindividual receive signal strength indicator RSSI value of a test signalreceived by said second station for each first antenna beam direction ofsaid first station; selecting a respective first antenna beam directionof said first station having the best received signal strength indicatorRSSI value for establishing the primary communication path; sending testsignals from said first station to said second station by using saidselected first antenna beam direction of said first station andreceiving said test signals by successively using all second antennabeam direction of said second station, wherein an individual receivesignal strength indicator RSSI value of said test signal received usinga respective second antenna beam direction of said second station isdetermined for each second antenna beam direction; and selecting arespective second antenna beam direction of said second station havingthe best receive signal strength indicator RSSI value for establishingthe primary communication path.
 24. A communication method according toclaim 23, wherein sending test signals from said first station to saidsecond station by successively using all first antenna beam directionsis performed by: sending a test signal from said first station to saidsecond station by using a first antenna beam direction of said firststation and a wide beam antenna of said second station; determining areceived signal strength indicator RSSI value of said test signal; andsending a further test signal from said first station to said secondstation by using another first antenna beam direction of said firststation, said test signal being received by said wide beam antenna ofsaid second station and determining another receive signal strengthindicator RSSI value of said further test signal until an individualreceive signal strength indicator RSSI value has been determined forevery first antenna beam direction of said first station.
 25. Acommunication method according to claim 23, wherein determining anindividual receive signal strength indicator RSSI value of a test signalreceived by a receiving station for each antenna beam direction of asending station comprises the transmission of the determined individualreceive signal strength indicator RSSI value from the receiving stationto the sending station.
 26. A communication method according to claim23, wherein the individual received signal strength indicator RSSIvalues determined for the individual first and second antenna beamdirections are stored in first and second RSSI tables, respectively. 27.A communication method according to claim 26, wherein establishing atleast one alternative communication path is performed by: determining arelative distance between a respective first/second antenna beamdirection used for said primary communication path and first/secondantenna beam directions of unused first/second antennas; identifyingfirst/second antenna beam directions of unused first and second antennashaving a sufficiently high received signal strength indicator RSSI valueand a sufficient distance relative to the respective first/secondantenna beam direction used for said primary communication path; andestablishing the at least one secondary communication path by using saididentified first and second antenna beam directions.
 28. A communicationmethod according to claim 27, wherein establishing the at least onealternative communication path by using said identified first and secondantenna beam directions is performed until no further first and secondantenna beam directions of unused first and second antennas having asufficiently high received signal strength indicator RSSI value and asufficient distance relative to the respective first/second antenna beamdirection used for said primary communication path can be identified.29. A communication method according to claim 21, wherein establishing aprimary communication path is initiated by: establishing a preliminarycommunication path between said first and second stations via a firstwide beam antenna of said first station and a wide beam antenna of saidsecond station to detect the presence of a respective first and secondstation.
 30. A communication method according to claim 21, furthercomprising: determining availability of the primary communication pathand of the at least one secondary communication path; using the primarycommunication path for wireless communication and returning to thedetermining if the primary communication path and the at least onesecondary communication path are available; using the primarycommunication path for wireless communication and establishing at leastone new secondary communication path if the primary communication pathis unavailable; using the secondary communication path for wirelesscommunication and establishing a new primary communication path if theprimary communication path is unavailable and the at least one secondarycommunication path is available; and returning to the establishing aprimary communication path if neither the primary communication path northe at least one secondary communication path is available.
 31. Acommunication method according to claim 30, wherein establishing a newprimary communication path is performed by using the respective firstand second antenna beam directions of unused first and second antennashaving the highest available signal strength indicator RSSI value.
 32. Acommunication method according to claim 21, wherein communicationbetween said first and second station via said primary and/or at leastone secondary communication path is a bi-directional wirelesstransmission using a transmission frequency of about 60 GHz.
 33. Acommunication method according to claim 21, further comprising:coherently combining information signals transmitted on the primarycommunication path and on each one of the at least one alternativecommunication path.
 34. A communication method according to claim 33,wherein the information signals transmitted on the primary communicationpath and on each one of the at least one alternative communication pathare the same.
 35. A communication method according to claim 21, furthercomprising: operating the second station as a RAKE receiver, whereineach second antenna used for establishing said primary communicationpath or said at least one alternative communication path corresponds toa finger of the RAKE receiver.
 36. A communication method according toclaim 21, wherein the second station comprises a RAKE receivercomprising a plurality of receiver chains and each second antenna isconnected to one receiver chain.
 37. A communication method according toclaim 21, wherein the second station comprises a switch network and aRAKE receiver comprising a plurality of receiver chains, the number ofchains being smaller than the number of the second narrow beam antennas,the method further comprising connecting each of second antenna used forestablishing said primary communication path or said at least onealternative communication path to one receiver chain.
 38. Anon-transitory computer-readable medium including computer program,which when executed by a first communication station, causes firstcommunication station to perform a method comprising: establishing aprimary communication path via a first one of a plurality of firstantennas of the first station and a first one of a plurality of secondantennas of a second station; and establishing at least one alternativecommunication path via said first one of said plurality of firstantennas and said first one of said plurality of second antennas whenthe primary communication path is blocked, wherein said at least onealternative communication path is different from said primarycommunication path.